1. Field of the Invention
This invention relates to endless conveyor belt systems and especially to accessory devices adapted for use with such systems and configured to be powered by the conveyor belt itself.
2. Discussion of Related Art
In coal mines and the like, endless belt conveyors are often used to transport the mined mineral from within the mine itself. Customarily, centrifugal switches are connected to the lower portion of the return belt of each conveyor to provide an indication of the operative condition of the particular belt in question. All mines use two of these switches on each belt operating in any sequence of belts. Often the belts are at 90.degree. angles to each other with a first belt dumping a load onto the next belt in line. On each belt line in the system, there is a large belt drive unit at the head end of the belt and a tail piece at the far end for the next belt to dump onto. One of the centrifugal switches is put just behind each drive unit on the return portion of the belt. This is for protection of the drive unit. In case the belt is overloaded and slows down, the switch opens, cutting power to the motor causing the belt drive to stop thereby preventing the motor from burning up. Another centrifugal switch is placed just ahead of each tail piece. When this switch is up to speed, it automatically starts the next succeeding belt drive. Thus, if any belt in the system stops, the centrifugal switches automatically stop all the drive units behind them, so that there will be no pile up of mined minerals on the tail piece of the belt that has stopped.
One system for connection of such centrifugal switches is to urge a roller against the bottom surface of the return belt of the endless conveyor. Such a system makes engagement between the centrifugal switch drive mechanism and the dirty side of the belt causing the drive mechanism to become clogged and eventually inoperative.
In order to avoid such deficiencies, it has been suggested to engage the centrifugal switch drive to the clean side of the belt. U.S. Pat. No. 4,088,222, issued May 9, 1978 to Hurt, shows a belt switch for an endless conveyor monitoring switch assembly which includes an elongated frame having a shaft journalled for rotation therein and extending longitudinally therealong. A drive wheel attached to and rotatable with the shaft at a first end of an elongated frame and a detecting switch is attached to the shaft at the opposite end of the elongated frame. A seesaw, U-shaped mounting member is attached to the elongated frame at a point intermediate the drive wheel of the detecting switch for mounting the elongated frame on an endless conveyor cable support. The mounting member allows the weight of the elongated frame and its attachment to pivot the frame in a seesaw manner to bring the drive wheel into contact with the lower surface of the upper belt of the conveyor. Other systems which show mounting and drive wheels for engagement with the clean side of a conveyor belt include U.S. Pat. No. 3,139,217, issued June 30, 1964 to Mell, and U.S. Pat. No. 1,973,312, issued Sept. 11, 1934 to Hardinge.